1. Field of the Invention
The present invention relates to a band-pass filter and, more particularly, to a method of producing a band-pass filter, for example, for use in a communication device operated in a micro-wave band to a millimeter-wave band and a band-pass filter.
2. Description of the Related Art
Conventionally, LC filters have been used as band-pass filters. FIG. 26 shows an equivalent circuit of a conventional LC filter.
The LC filter includes first and second resonators 101 and 102. The resonators 101 and 102 each include a capacitor C and an inductance L connected in parallel to each other. Conventionally, to define the LC filter as a single electronic component, a monolithic capacitor and a monolithic inductor are integrated with each other. In particular, to achieve the circuit configuration shown in FIG. 26, two resonators each including a monolithic capacitor component and a monolithic inductor component are provided as one monolithic electronic component. In the LC filter, two resonators 101 and 102 are coupled to each other via a coupling capacitor C1.
When the LC filter having the circuit configuration shown in FIG. 26 is provided as a single component, it is necessary to provide many conductor patterns and via-hole electrodes for connecting the conductor patterns to each other. Accordingly, to obtain a desired characteristic, the above conductor patterns and via-hole electrodes must be formed with high accuracy.
As described above, to form the LC filter, many electronic elements are required. Accordingly, the LC filter has a complicated configuration, and the size of the LC filter cannot be substantially reduced. In addition, the resonance frequencies of LC filters are generally expressed as f=xc2xdxcfx80(LC)xc2xd, in which L represents the inductance of a resonator, and C represents the capacitance thereof. Accordingly, to obtain an LC filter that operates at a high frequency, it is necessary to reduce the product of the capacitor C of the resonator and the inductance L. That is, for production of an LC filter that operates at a high frequency, it is necessary to reduce errors, caused in the production of the inductance L and the capacitance C of the resonator. Accordingly, to develop a resonator that operates at a still higher frequency, the accuracy of the above many conductor patterns and via-hole electrodes as described above must be further enhanced. Thus, development of LC filters for use at a higher frequency has been very difficult.
To overcome the above-described problems, preferred embodiments of the present invention provide a method of producing a band-pass filter in which the above-described technical difficulties are greatly reduced, and the band-pass filter which operates at a high frequency is easily produced, miniaturization of the band-pass filter is easily performed, and for which control conditions of dimensional accuracy are greatly relaxed, and a band-pass filter.
According to preferred embodiments of the present invention, a method of producing a band-pass filter is provided which includes the steps of selecting the shape of a metallic film and the connection points of input-output coupling circuits with respect to the metallic film such that first and second resonance modes are generated in the metallic film, the metallic film is provided on a surface of a dielectric substrate or inside of the dielectric substrate, and discontinuous providing at least a portion of the resonance current and the resonance electric field in at least one of the resonance modes such that the first and second resonance modes are coupled.
Preferably, in the step in which the first and second resonance modes are coupled, at least a portion of the resonance current in at least one of the resonance modes is discontinuous.
Also preferably, in the step in which the first and second resonance modes are coupled, at least a portion of the resonance current in at least one of the resonance modes is discontinuous.
According to preferred embodiments of the present invention, a band-pass filter is provided which includes a dielectric substrate, one metallic film provided on a surface of the dielectric substrate or inside of the dielectric substrate, input-output coupling circuits connected to first and second portions of the periphery of the metallic film, the shape of the metallic film and the positions of the connection points of the input-output coupling circuits are selected such that the first resonance mode propagated substantially in parallel to the imaginary straight line passing through the connection points of the input-output coupling circuits, and the second resonance mode propagated substantially in the perpendicular direction of the imaginary straight line are generated, and a coupling mechanism for discontinuously providing at least a portion of the resonance current or resonance electric field whereby the first and second resonance modes are coupled to each other.
Preferably, the coupling mechanism is a resonance current control mechanism for discontinuously providing at least a portion of the resonance current in at least one of the resonance modes.
The resonance current control mechanism may be an opening provided in the metallic film.
Preferably, the coupling mechanism is a resonance electric field control mechanism for controlling the resonance electric field in at least one of the resonance modes.
The resonance electric field control mechanism may be a resonance electric field control electrode arranged opposed to the metallic film through at least a portion of the layers of the dielectric substrate.
Other features, characteristics, elements and advantages of the present invention will become apparent from the following description of preferred embodiments thereof with reference to the attached drawings.